1. Field of the Invention
The present invention relates to a discharge tube, and more particularly to a discharge tube having a stabilized discharge inception characteristics suitably used for a voltage controller, a gap switch, a sharpener gap and so on.
2. Description of the Invention
Generally, a discharge tube is adopted in a voltage controlling device, or in a gap switch for correctly controlling a discharge inception of a pulse laser or the like, and as a discharge tube suitable for this purpose there has been provided a discharge tube which comprises a cylindrical container made of an insulation tube provided with a pair of discharge electrodes at opposite sides thereof, and having an inert gas sealed therein.
The discharge tube as constructed above in general has a tendency that when the frequency of repetitive discharge becomes low, a discharge inception is delayed and a discharge inception voltage is thereby raised. However, it is not desirable that the discharge inception voltage changes according to the discharge frequency, and in fact, a discharge inception voltage in a discharge tube should be stabilized regardless of the above frequency of repetitive discharge.
In view of these defects to be overcome, there has been invented a discharge tube which is capable of accelerating an inception of the main discharge by providing trigger lines made of conductive layers or the like respectively extending from opposite electrodes on the inner surface of a cylindrical container which is a main body of the discharge tube. However, in the discharge tube as constructed above, when the discharge is repeated for a long time, the trigger lines are worn and thereby the trigger effect thereof does not last long, and in addition, an abnormal discharge creeping, that is, so called an inner creeping discharge along the inner surface of the cylindrical container is likely to occur.
In view of the above phenomena, there has also been proposed a discharge tube which is capable of accelerating a preionization of the gas sealed in a discharge space thereof, avoiding thereby the delay of an inception of discharge even when the frequency of repetitive discharge is substantially low, for example, by dispersively building up a small amount of electrically conductive substance on the inner surface of the cylindrical container (as shown in Japanese Patent Application Laid-open No. 3-68389), or by coating an insulation coating substance containing a gasionization accelerator such as a silicate compound of alkaline metal on the inner surface of the cylinder (as shown in Japanese Patent Application Laid-open No. 4-133244). However, even a discharge tube as constructed above could not perfectly solve such a problem that the inner creeping discharge is more likely to occur in proportion to the cumulative number of discharge, in spite of the fact that it is provided with a stabilized discharge inception.
The present invention has been made to eliminate such problems, and it is an object of the present invention to provide a discharge tube which has a stabilized discharge inception characteristics regardless of the frequency of repetitive discharge or of the cumulative number of discharge, yet capable of eliminating an occurrence of inner creeping discharge by building up a gas ionization accelerator at specified regions within the cylindrical container.